The present invention relates to a solid state image pickup device, and, in particular, to a solid state image pickup device in which a signal processing circuit including a capacitor is provided for each of pixel columns in a pixel array unit where pixels are arranged in a matrix pattern, each pixel including a photoelectric converting element.
A solid state image pickup device in which pixels are arranged in a matrix pattern, each pixel including a photoelectric converting element, may be classified into a charge-transfer solid state image pickup device represented by a CCD (charge coupled device) image sensor; or an XY-address solid state image pickup device such as a MOS (metal oxide semiconductor) image sensor, e.g., a CMOS (complementary metal oxide semiconductor) image sensor.
Further, an CCD image sensor may be classified into a horizontal CCD image sensor or a horizontal scanning CCD image sensor. In a horizontal CCD image sensor, a signal charge obtained by photoelectric conversion in a pixel is vertically transferred by a vertical CCD, which is provided for each pixel column in the CCD image sensor, and the signal charge is horizontally transferred by a horizontal CCD. Then, a charge detecting unit provided at an end portion of a transfer destination of the horizontal CCD performs voltage conversion, and each obtained signal voltage is sequentially read. In a horizontal scanning CCD image sensor, a signal charge obtained by photoelectric conversion in a pixel is vertically transferred by a vertical CCD, which is provided for each of pixel column in the CCD image sensor, and a charge detecting unit provided in a subsequent stage of the vertical CCD in each vertical pixel column performs voltage conversion. Accordingly, each obtained signal voltage is sequentially read by horizontal scanning.
In a conventional MOS image sensor and in a conventional horizontal scanning CCD image sensor, a signal processing circuit including a CDS (correlated double sampling) circuit or the like for removing fixed pattern noise of pixels is provided for each of vertical pixel column in the respective image sensor. Alternatively, the signal processing circuit may include an A/D (analog/digital) converter, which is also provided for each vertical pixel column.
In a conventional MOS image sensor, a signal processing circuit including a CDS circuit or the like may connect to one end of each of vertical signal lines. Therefore, the number of signal processing circuits is the same as that of pixel columns. If a pixel array unit of a conventional MOS image sensor is miniaturized to reduce a chip size, each signal processing circuit typically needs to be miniaturized accordingly. Capacitors are often indispensable for performing CDS processing or A/D conversion in a signal processing circuit for a conventional MOS image sensor, and thus the capacitors occupy a large area of the circuit. Therefore, if a scale of the signal processing circuit should be reduced in accordance with miniaturization of the pixel array unit, the area occupied by the capacitors needs to be reduced.
However, a smaller area occupied by the capacitors leads to a smaller capacitance. In the above-mentioned conventional CDS circuit or the A/D converter, noise is typically removed more effectively as a capacitance of a capacitor is increased. Therefore, an area occupied by a respective capacitor used for CDS or A/D converter noise removing processing should not be reduced to maintain noise removing effects of the CDS or A/D converter. Further, when a pixel pitch is reduced, the width of a capacitor in the signal processing circuit typically must also be reduced. As a result of this configuration, when a predetermined insulating space is secured between signal processing circuits in adjoining vertical pixel columns, a total capacitor area often increases.
When implementing a conventional CDS circuit, if an increased number of pixels are used for achieving higher resolution, the number of columns and the number of signal processing circuits increase, which increases output loads. Accordingly, a capacitor of a larger capacitance is required. However, as described above, an area occupied by the capacitor also increases as the capacitance increases.